Concrete structures are often formed in situ by pouring a cementitious slurry into forms and allowing the slurry to cure into a solid concrete. The slurry composition is formulated based on the desired properties for the structure being formed with the cement. For example, a sidewalk, a highway, and a foundation for a high-rise building would have different strength and load requirements. Also, it may be desirable to control the viscosity of the slurry, depending on whether the slurry is to be poured adjacent the truck or if it must be pumped some distance, such as from the street to the back of a building, as well as how quickly the slurry should solidify and cure. It is important to formulate the slurry appropriately, including adding the correct quantity of water to the dry materials to obtain a concrete mixture with the desired viscosity and curing properties.
Commonly, cement trucks are used to prepare and deliver cement slurries to construction sites. The trucks generally include a rotatable barrel in which water, cement, sand or gravel, and other additives are mixed. Underneath the barrel, there is a pressurized water tank, and a pipeline connects the water tank to the barrel. A valve in the pipeline controls the amount of water added to the solid materials in the barrel. Generally, the valve is manually operated, with a gauge or other visual indicator located inside the cab of the truck showing the volume of water delivered to the barrel or the viscosity of the mixture in the barrel. Some newer model trucks include electrically operated solenoid valves.
However, the gauge or other indicator in the cab only provides information to the truck operator when the operator pays attention to it. It is easy for an operator to get distracted from watching the gauge, such as by a phone call, a conversation, or becoming lost in thought, thus allowing too much water to flow into the barrel. If too much water is added, the slurry is ruined and must be discarded. As a result, additional materials are needed for a new load of cement and additives, and construction may be delayed while the operator drives to the source of the dry materials, reloads the barrel and the water tank, and returns to the construction site. Further, the use of additional materials increases project costs.
The amount of water needed for each job is variable, depending on the quantity of dry materials, the moisture content of the dry materials, and the requirements of the particular job. Thus, it difficult to predict the amount of water needed and, therefore, also difficult to set up a reliable automated control system for water flow. Thus, there is a need for an additional system to aid in preventing the addition of excessive quantities of water to cement slurries.